Biocidal Activity of the Bacillus thuringiensis 3D Cry Toxins, Molecular Crosstalk at the Insect Midgut with Implication in Insect Resistance Development

Bacillus thuringiensis (Bt) is a Gram-positive bacteria characterized by the production of parasporal crystalline proteins toxic to a wide range of insect orders.Cry toxins targeted pests of crops of economic importance.Nowadays, around 600 genes encode crystalline proteins with a range of molecular weight of 50 to 130 kDa.Cry proteins are comprised of three domains and their tridimensional structures have been elucidated by X-rays.Their mode of action remains to be defined and understood.However, most of these proteins follow a basic program for their biocidal activity.A critical step in the mode of action of the 3D Cry toxins is the specific binding to the receptors present in the midgut epithelial.These receptors are determinants of the specificity and susceptibility of targeted insects.Among them are the classical glycosyl phosphate inositol (GPI)-anchored membrane receptors, such as N-aminopeptidase, Alkaline Phosphatase, and classical epithelial cadherins DE-Cadherins.The second group of binding proteins includes ABC transporters, V-ATPase, and other lipid rafts-associated proteins.The hallmark of this molecular crosstalk at the insect midgut is that it is conserved between different Cry 3D toxins with diverse targets of insects.Moreover, the receptors in this tissue are also common resulting in a common mode of action that comprises the insect response to entomopathogens, which potentially can guide a design of safe and integrated management of crop pests.